1. Field of the Invention
The present invention relates to a stereoscopic 3D display device, and more particularly, to a glasses-free autostereoscopic 3D display device.
2. Description of the Related Art
Three-dimensional (3D) display may be briefly defined as “all types of systems for artificially generating a 3D screen.”
Here, a system may include software technologies that generate content viewable as three-dimensional images and hardware for actually implementing 3D content made by the software technologies. As described above, the system includes a software region because content configured with a particular software scheme is separately required for each stereoscopic implementation process in the case of 3D display hardware.
Furthermore, virtual 3D display (hereinafter, referred to as a stereoscopic 3D display device) may be defined as all types of systems for allowing a user to virtually experience depth in the planar display hardware using binocular disparity due to our eyes being separated from each other by about 65 mm in the horizontal direction among various factors for allowing a person to experience a three-dimensional effect. In other words, our eyes view slightly different images (strictly speaking, left and right spatial information being slightly divided) even when viewing the same object due to binocular disparity, and if those two images are transmitted to the brain through the retina, then the brain fuses two images together in a correct manner to allow us to experience depth. Using this phenomenon, a stereoscopic 3D display device implements virtual depth through a design of displaying the left and right images at the same time on a two-dimensional display device and sending them to each eye.
In order to display two channel images on a screen in the stereoscopic 3D display device, for example, each channel is outputted by changing each row in one direction (horizontal or vertical) on a screen. In this manner, when two channel images are outputted at the same time on a display device, the right image enters into the right eye and the left image enters into the left eye as they are in the case of a glasses-free type hardware structure. Furthermore, in the case of a glasses-wearing type, a method is used to hide the right image from the left eye and hide the left image from the right eye, through specific glasses suitable for this purpose.
An important factor for allowing a person to experience stereoscopic and depth effects may be binocular disparity due to a distance between two eyes, but depth effects are also closely related to psychological and memory factors. Therefore, 3D implementation methods are typically divided into a volumetric type, a holographic type, and a stereoscopic type based on the level of three-dimensional image information provided to an observer.
The volumetric type as a method of experiencing a perspective in a depth direction uses a psychological factor, and a suction effect may be applicable to 3D computer graphics in which perspective projection, overlapping, shadow, luminance, movement, and the like are shown based on corresponding calculations, and so-called IMAX cinemas in which a large-sized screen having a wide viewing angle is provided to an observer to evoke an optical illusion and create the feeling of being sucked into a space.
The holographic type, known as the most complete 3D implementation technique, may be represented by laser beam reproduction holography or white light reproduction holography.
Furthermore, the stereoscopic type as a method of experiencing a stereoscopic effect uses the binocular physiological factor. Using the brain's capacity of generating spatial information prior to and subsequent to a display plane, a stereoscopic effect is experienced when the brain combines associative images of a plane including parallex information seen by the left and right eyes, separated from each other by about 65 mm as described above, namely, stereography. The stereoscopic type may be largely divided into a glasses-wearing type and a glasses-free type.
A representative method known as the glasses-free type may include a lenticular lens mode and a parallex barrier mode in which a lenticular lens sheet on which cylindrical lenses are vertically arranged is provided at a front side of the image panel.
FIG. 1 is a view for explaining the concept of a typical lenticular lens type stereoscopic 3D display device in which a relationship between the rear surface distance (S) and the viewing distance (d) is shown.
Furthermore, FIG. 2 is a view illustrating a lenticular lens type stereoscopic 3D display device and a light profile as an example.
Here, viewing diamonds, light profiles, and view data forming a viewing zone are illustrated at the center of FIG. 2, and an actually perceived view is schematically illustrated at the bottom of FIG. 2.
Referring to FIGS. 1 and 2, a typical lenticular lens type stereoscopic 3D display device may include an upper and a lower substrate, a liquid crystal panel 10 filled with liquid crystals therebetween, a backlight unit (not shown) located on a rear surface of the liquid crystal panel 10 to irradiate light, and a lenticular lens sheet 20 located on a front surface of the liquid crystal panel 10 to implement a stereoscopic image.
The lenticular lens sheet 20 is formed with a plurality of lenticular lenses 25, an upper surface of which is made of a convex lens shaped material layer on a flat substrate.
The lenticular lens sheet 20 performs the role of dividing left-eye and right-eye images, and diamond shaped viewing diamonds (normal view zone) 30 in which images corresponding to the left-eye and right-eye are viewable by the left-eye and right-eye, respectively, are formed at an optimal 3D distance (d) from the lenticular lens sheet 20.
The width of one viewing diamond 30 is formed with the viewer's interocular distance (e) to perceive parallax images entering the viewer's left-eye and right-eye as a stereoscopic image.
Here, each viewing diamond 30 is formed with the corresponding sub-pixel view data, namely, image, of the liquid crystal panel 10.
View data denotes an image captured by cameras separated by a reference measure of the interocular distance (e).
In such a typical lenticular lens type stereoscopic 3D display device, the liquid crystal panel 10 and lenticular lens sheet 20 are supported by a mechanical body (not shown), and the liquid crystal panel 10 and lenticular lens sheet 20 are separated by a predetermined distance (rear surface distance; S).
Here, an intervening layer 26 (e.g., a gap glass) is inserted into the typical lenticular lens type stereoscopic 3D display device to constantly maintain the rear surface distance (S).
Since a lenticular lens type stereoscopic 3D display device is implemented in a multi-view mode formed based on an initially designed view map, the viewer may view a 3D image when entering a predetermined view zone.
Here, referring to a light profile measured at an optimal viewing distance (d) with reference to FIG. 2, it is seen that the intensity of light is the highest at the center of the viewing diamond 30 and gradually reduces towards the end of the viewing diamond 30. A difference between the maximum and minimum of the intensity of light may be defined as a luminance difference (LD) (ΔL), and typical lenticular lens type stereoscopic 3D display devices show a large luminance difference, thereby having a significant effect on their image quality.
On the other hand, an image difference between views perceived as the user's location moves between the viewing diamonds 30 is called image flipping, and the maximum difference is perceived when moving from a normal view to a reversed view, or vice versa. Accordingly, an image difference between first view data and last view data increases as the number of views increases, thereby deteriorating the phenomenon of image flipping.